This isn't the same as with systemd timer because timer lets you specify when you want to run your service exactly and will fallback to running when the system comes online. With @hourly I lose this control and multiple machines could potentially trigger backups at the same time, hogging the physical hard drives and the network.
That isn't something I'd want to happen, it sounds like it creates a potential queue of scripts that will flood the system on start, if it works the way you described.
I prefer the deterministic behavior of cron, the script will run when it is specified to run, as you said earlier, as long as the system is running; and as I stated in a separate comment, it will run @reboot if I need it to run then.
> With @hourly I lose this control and multiple machines could potentially trigger backups at the same time
Then don't use @hourly, use staggered times, it's very easy.
This isn't what happens. If you leave it offline for days it'll only trigger the service only a single time.
100 jobs all running at different times throughout the week is a very different load than them all falling back and running at the same time on system boot.
There are two options to fix it;
Disable persist so no catching up on missing scripts. Set OnBoot=5m so it gets ran 5 minutes after boot, so your script (say backup) is ran on boot first, then every time on schedule
Enable persist but just add sleep in ExecStartPre - very "cron" way but there is just no in-systemd option to enable "catch up" script to be delayed
Sadly no option to "run catch-up timers with delay" at least yet
> Then don't use @hourly, use staggered times, it's very easy.
Not in cron. In systemd it's just RandomizedOffsetSec=30m and it is "stable" - same host with same job will always have same delay so on multiple hosts it is spread nicely. There is also non-stable version